Corn Poppy (Papaver rhoeas) is a dicot plant in the papaveraceae family. A single amino acid substitution from Proline 197 to Alanine has led to resistance to ALS inhibitors as indicated in the table below.

BACKGROUND: Papaver rhoeas (L.) has evolved resistance to tribenuron in winter wheat fields in northern Greece owing to multiple Pro197 substitutions. Therefore, the cross-resistance pattern to other sulfonylurea and non-sulfonylurea ALS-inhibiting herbicides of the tribenuron resistant (R) and susceptible (S) corn poppy populations was studied by using whole-plant trials and in vitro ALS catalytic activity assays. RESULTS: The whole-plant trials revealed that tribenuron R populations were also cross-resistant to sulfonylureas mesosulfuron+iodosulfuron, chlorsulfuron and triasulfuron. The whole-plant resistance factors (RFs) calculated for pyrithiobac, imazamox and florasulam ranged from 12.4 to >88, from 1.5 to 28.3 and from 5.6 to 25.4, respectively, and were lower than the respective tribenuron RF values (137 to >2400). The ALS activity assay showed higher resistance of the ALS enzyme to sulfonylurea herbicides (tribenuron > chlorsulfuron) and lower resistance to non-sulfonylurea ALS-inhibiting herbicides (pyrithiobac > florasulam ~ imazamox). CONCLUSION: These findings indicate that Pro197 substitution by Ala, Ser, Arg or Thr in corn poppy results in a less sensitive ALS enzyme to sulfonylurea herbicides than to other ALS-inhibiting herbicides. The continued use of sulfonylurea herbicides led to cross-resistance to all ALS-inhibiting herbicides, making their use impossible in corn poppy resistance management programmes..

Variations in the acetolactate synthase (ALS) gene sequence were determined from 28 populations of corn poppy resistant (R) to tribenuron and from 6 populations susceptible (S) to this herbicide. The ALS gene fragment (634 bp) sequence revealed in R populations five point mutations at the codon Pro197, and among them the substitution of Pro197 by Ala was the most common. The sequencing chromatograms revealed that nine R individuals had only the mutant ALS gene and were homozygous (RR), 18 R individuals had both the wild type and the mutant ALS gene and were heterozygous (RS), whereas one R individual was heterozygous but with two different mutant ALS alleles (R1R2). The use of restriction digestion profile analysis to verify the DNA sequence results by detecting the existence of point mutations at the codon 197 managed to distinguish the R and S alleles and confirmed the results obtained from the sequencing chromatograms analysis. The secondary protein structure prediction suggested the formation of novel β-strands for each of the five mentioned amino acid substitutions that was not present in wild type ALS around the mutant site. These findings support the hypothesis that the substitution of Pro197 by Ser, Thr, Ala, Arg, or Leu resulted in altered secondary structure, which stabilizes an ALS tertiary conformation that prevents tribenuron binding and thus confers resistance to this herbicide..